Implantable medical devices may be used to deliver therapeutic electrical stimulation to patients to treat a variety of symptoms or conditions, such as chronic pain, tremor, Parkinson's disease, epilepsy, cardiac arrhythmia, incontinence, sexual dysfunction, or gastroparesis. In order to treat such symptoms or conditions, an implantable medical device may deliver stimulation via electrical leads that include electrodes located proximate to the “target tissue” for receipt of the stimulation. The target tissue is typically muscle or nerve tissue. As examples, the target tissue may be within or near the spinal cord, heart, cranial nerves, pelvic nerves, gastrointestinal tract, or brain of a patient.
The lead-borne electrodes located proximate to one or more target tissue sites may be referred to as a lead-borne electrode array. In addition to a lead-borne electrode array, many implantable medical devices include device or implant site electrodes, i.e., one or more electrodes proximate to the implantable medical device when implanted relative to the distally-located, lead-borne electrode array. For example, implantable medical devices may use one or more electrodes on their housing, or the housing itself, as an indifferent electrode, i.e., anode, for therapeutic stimulation or other functions.
In general, implantable medical devices deliver stimulation in the form of electrical pulses. At any given time, an implantable medical device may deliver stimulation according to one or more programs, each program including respective values for each of a plurality of stimulation parameters, such as voltage or current pulse amplitude, pulse width, pulse rate and duty cycle. A program may also include an electrode configuration, which identifies electrodes selected for delivery of stimulation and their polarities, i.e., cathode or anode. A group of stimulation parameter values may be referred to as a “program” in the sense that they drive the stimulation therapy to be delivered to the patient.
Implantable medical devices may provide alarms, alerts, reminders or other notifications to a patient for a variety of reasons. As examples, implantable medical devices may provide notifications to a patient for low battery conditions, battery end-of-life conditions, or as a reminder to recharge a battery of the implantable medical device. As other examples, implantable medical devices may provide notifications for lead faults, memory faults, or other device faults. Further, implantable medical devices may provide notifications in response to detected events relevant to the condition of the patient, such as seizures or cardiac arrhythmias, notifications of upcoming therapies, such as defibrillation shocks, or reminders to take concurrent therapies not provided by the implantable medical device, such as one or more drugs. Such notifications are often delivered via audible sounds or tactile vibrations, but in some cases, electrical stimulation has also been used to deliver patient notification.